The invention relates generally to a drill having a specialized drill point for boring holes into metals. More specifically the invention relates to a drill having a web-thinning V-notch and aggressive geometry allowing improved centering, faster penetration of the work piece, faster cutting speeds, and improved chip forming geometry.
A wide variety of drill point styles are known and particularly adapted for specific drilling tasks. For example, the 118 degree general purpose drill bit is the most commonly used drill point and gives satisfactory results in a wide variety of materials. Another type is the xe2x80x9cRaconxe2x80x9d, or radiused conventional point which forms a relatively large arc with its curved lips and has a rounded lip corner reducing corner wear and eliminating burrs at exit. Split point, or crankshaft drill points are known in the art for being self-centering and requiring less torque and thrust during drilling. The Double Angle point is used in drilling of abrasive materials. The double angle on this point acts as a chamber concentrating tool wear along the entire cutting lip and reducing corner wear. A helical drill point has a xe2x80x9cSxe2x80x9d shaped chisel making the point self-centering and requiring less torque and thrust.
Regardless of the shape of the chisel or lip curvature, the life of the drill point depends on how well the point dissipates heat. If the point does not adequately conduct heat away from its cutting edges, the temperature buildup will xe2x80x9cburnxe2x80x9d the point and diminish the life of the drill bit. The heat generated at the lip of the drill point is directly related to the load and stresses the lip is subjected to. The more efficiently load stresses are dissipated, the less heat is built up at the cutting edge of the drill point. The Racon point mentioned above attempts to minimize stress by curving the cutting lip. Although this point does offer an improvement, heat dissipation and wear are still critical concerns in the art.
A problem with these drills is that the center of the drill point at the intersection of the two cutting surfaces forms a chisel. The chisel edges resemble the center ridge of a roof, and cannot be made sharp in the sense that the cutting edges of the drill can be made sharp. The chisel edge is also the most slowly moving part of the drill, being nearest to the center. This combination of inherent dullness and slow speed means that the chisel edges do not so much cut a chip as they plow up or extrude a chip ahead of them. This extruded workpiece material tends to build up in front of the chisel edge, wearing it more quickly than the faster moving and sharper main cutting edges. In order to minimize the effect of the chisel, prior art drill points have been formed with a web thinning gash or notch which reduces the length of the chisel point. However, these notches formed a negative or neutral cutting angle adjacent to the main cutting edge. While generally an improvement, a portion of the main cutting edge was lost and replaced with a longer, but less effective cutting edge. Therefore, there remains a need in the art for a drill having a shorter chisel without an accompanying loss of effective cutting edge surface.
An object of the present invention to provide an aggressive drill point geometry for a drill. These and other advantages are provided by a drill comprising a drill body having at least two helical flutes, a pair of cutting surfaces on an end of the drill body, each cutting surface having an associated land formed thereon, a web formed between the two cutting edges, and a web thinning notch formed on either side of the web, wherein each notch forms a notch cutting edge having a positive rake angle.